Applanation detection system for a non-contact tonometer

Abstract

A non-contact tonometer is improved by providing a non-telecentric applanation detection system enabling relaxation of instrument alignment requirements during testing. In a preferred embodiment, the applanation detection system comprises an emitter for directing an obliquely incident beam of light for reflection by the cornea, and a detector array having a plurality of photosensitive detector array elements located to receive corneally reflected light. The detector array generates a plurality of signal curves for light energy received at different locations on the array as a function of time, and the signal curves are evaluated to determine an optimal signal curve which best indicates the moment of applanation.

What is claimed is: 
     
       1. A non-contact tonometer for measuring intraocular pressure of a patient's eye comprising: a test axis;   fluid pulse means for generating a fluid pulse of increasing force and discharging said fluid pulse along said test axis toward said eye to progressively deform a cornea of said eye to achieve a state of corneal applanation;   applanation detection means for monitoring deformation of said cornea caused by said fluid pulse, said applanation detection means including an emitter on one side of said test axis for directing an incident beam of light to said cornea for reflection by said cornea and a detector array on another side of said test axis, said detector array having a plurality of photosensitive detector array elements for receiving light reflected by said cornea and generating a plurality of primary signal curves representative of the intensity of light received by said detector array at a plurality of different array locations as a function of time; and   evaluation means for determining an optimal signal curve from said plurality of primary signal curves and calculating said intraocular pressure from said optimal signal curve.   
     
     
       2. The non-contact tonometer according to claim 1, wherein there is only one said emitter. 
     
     
       3. The non-contact tonometer according to claim 1, wherein said detector array is sampled at a predetermined frequency. 
     
     
       4. The non-contact tonometer according to claim 1, wherein said detector array is a photodiode detector array. 
     
     
       5. The non-contact tonometer according to claim 4, wherein said detector array is a four-by-four array having sixteen photodiode elements. 
     
     
       6. The non-contact tonometer according to claim 1, wherein said evaluation means includes a peak detector circuit for determining said optimal signal curve. 
     
     
       7. The non-contact tonometer according to claim 1, wherein said evaluation means includes memory means for storing said plurality of primary signal curves. 
     
     
       8. The non-contact tonometer according to claim 7, wherein said evaluation means combines said signal curve information from subgroups of adjacent elements in said detector array to provide a plurality of secondary signal curves representative of the intensity of light received by said detector array at a plurality of different border locations on said detector array as a function of time, and said evaluation means determines said optimal signal curve from said plurality of primary signal curves and said plurality of secondary signal curves. 
     
     
       9. The non-contact tonometer according to claim 8, wherein said detector array is a four-by-four array having sixteen photodiode elements. 
     
     
       10. The non-contact tonometer according to claim 9, wherein there are sixteen primary signal curves and thirty-three secondary signal curves. 
     
     
       11. The non-contact tonometer according to claim 1, wherein said applanation detection means further includes a beam contractor in front of said detector array. 
     
     
       12. The non-contact tonometer according to claim 1, wherein said applanation detection means further includes a lens array and an associated pinhole aperture array in front of said detector array. 
     
     
       13. The non-contact tonometer according to claim 11, wherein said applanation detection means further includes a lens array and an associated pinhole aperture array between said beam contractor and said detector array.